Electrolytic cell having metal electrodes

ABSTRACT

Disclosed is a bipolar electrolyzer useful for the electrolysis of alkali metal halides to yield alkali metal halates. The electrolyzer contains a series of individual bipolar units. Each of the individual bipolar units has a backplate with a cathodic surface, and cathodes extending from the cathodic surface. The opposite surface of the backplate is an anodic surface with anodes extending from the anodic surface. The anode assembly of the halate cell of this invention has an electrolyte resistant base member extending from the anodic side of the backplate. The electrolyte resistant base member has finger-like metal anodes mounted on and extending from one side and an electroconductive, hydrogen impermeable member bonded to the opposite side. The electroconductive, hydrogen impermeable member corresponds to an aperture in the backplate. A threaded bolt extends from the hydrogen impermeable member through the aperture in the backplate to the cathodic surface of the backplate. By maintaining a suitable tension on the threaded bolt, an electrolyte tight seal is maintained between the backplate and the electrolyte resistant anode base member.

United States Patent 1191 Raetzsch et al.

[ 1 May 20, 1975 ELECTROLYTIC CELL HAVING METAL ELECTRODES [75] Inventors: Carl W. Raetzsch; Hugh Cunningham, both of Corpus Christi, Tex.

[73] Assignee: PPG Industries, Inc., Pittsburgh, Pa.

[22] Filed: Nov. 30, 1973 21 Appl. No.: 420,744

Primary ExaminerJohn H. Mack Assistant Examiner-W. I. Solomon Attorney, Agent, or FirmRichard M. Goldman [57] ABSTRACT Disclosed is a bipolar electrolyzer useful for the electrolysis of alkali metal halides to yield alkali metal halates. The electrolyzer contains a series of individual bipolar units. Each of the individual bipolar units has a backplate with a cathodic surface, and cathodes extending from the cathodic surface. The opposite surface of the backplate is an anodic surface with anodes extending from the anodic surface. The anode assembly of the halate cell of this invention has an electrolyte resistant base member extending from the anodic side of the backplate. The electrolyte resistant base member has finger-like metal anodes mounted on and extending from one side and an electroconductive, hydrogen impermeable member bonded to the opposite side. The electroconductive, hydrogen impermeable member corresponds to an aperture in the backplate. A threaded bolt extends from the hydrogen impermeable member through the aperture in the backplate to the cathodic surface of the backplate. By maintaining a suitable tension on the threaded bolt, an electrolyte tight seal is maintained between the backplate and the electrolyte resistant anode base member.

6 Claims, 4 Drawing Figures I I I mgmgumzoims SHEET 10F 4.

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azuazms HAYNES SHEET 30F 4 ELECTROLYTIC CELL HAVING METAL ELECTRODES BACKGROUND OF THE INVENTION Alkali metal halates may be produced by the electrolysis of alkali metal halides. In the electrolytic production of alkali metal halates, for example, alkali metal chlorates, an alkali metal chloride brine is fed to an electrolytic cell. Chlorine is evolved as the anode and hydroxyl ion is present in electrolyte. The chlorine and hydroxyl ion come into contact and react according to the following formula:

C1 H (Cl O) C1 H O (i) thereby forming hypochlorite ions. The hypochlorite ion, in which the chlorine has a valence of +1, may be self-oxidized to a chlorite ion, in which the chlorine has a valence of +3, and a chloride ion, in which the chlorine has a valence of 1, according to the following reaction:

(Cl O) (CI O) (Cl O Cl (ii) The chlorite ion is further oxidized by hypochlorite ion to yield chlorate ion, in which the chlorine has a valence of +5, according to the following reaction:

(Cl O (CI OY (CI 'O Y Cl (iii) The starting point of the alkali metal halate process is the alkali metal halide. The halide has a valence of 1, therefore, the necessary valence change for the production of alkali metal halate is from 1' to +5, a total of +6. Six Faradays are required to produce 1 equivalent of alkali metal halate.

When an acid solution of alkali metal halide is electrolyzed, a hypochlorite solution is first formed containing little free hypohalous acid. Hydrochloric acid may be added to the electrolyte, increasing the concentration of the hypohalous acid. The oxidation 'of the hypohalous acid by hypohalite ions produces halates, the halogen, and hydrogen. Hydrogen ions then give more hypohalous acid and the process continues with the formation of halate ion in all parts of the electrolyte. Chemical formation of halate ion takes place not only in the volumes adjacent to the electrodes but throughout the entire cell.

In the operation of sodium chlorate cells, sodium chloride salt, purified to substantial freedom from heavy metal ion, such as magnesium ion, is fed to the cell. In the electrolytic cells of the prior art low current densities, e.g., less than about 100 amperes per square foot, provided an operating temperature of about 50C to about 65C. In such cells, solid sodium chloride has to be continuously added to the cell.

In a batch chlorate cell operation, after the cell liquor is recovered from the cell, it is clarified, e.g., by filtration, and then fed to an evaporating means for concentration. Afterwards, separation occurs and crystallized sodium chlorate crystals are recovered. Additionally centrifuge means may be used for further separation. In a continuous chlorate cell process, the cell liquor is cooled to crystallize the sodium chlorate and then returned directly to the cell without evaporation or re moval of the sodium chloride.

The cell liquor may be returned to saturating means SUMMARY OF THE INVENTION It has now been found that bipolar halate cells having fingered bipolar electrodes provide a compact electrolysis volume while permitting the use of large cell bodies, characterized by large electrolyte volumes. In this way, a small volume is utilized for electrolysis, while a large volume is provided for the chemical formation of halate ion. Because of the increased temperature of the electrolyte, due to the higher current densities obtained with metal electrodes, the solubility of alkali metal halates in cell liquor is increased. The large cell liquor volume relative to electrode volume, provides a longer cell residence time. The combination of higher halate solubility and longer residence time permits a higher concentration of halate ion in the cell liquor. This longer residence time allows more of the halate to be formed by chemical reaction rather than by electrolysis, thereby providing a higher current efficiency. The higher temperature also allows brine feed rather than solid salt feed to be utilized.

According to this invention, a bipolar alkali metal halate cell is provided having a plurality of individual bipolar units electrically in series. Each bipolar unit includes a backplate with a cathodic surface, and an anodic surface having an electrolyte resistant material on for adjustment to the desired strength and volume and returned to the cell.

the anodic surface. The cathodes are mounted on a cathodic side of the backplate and the anodes are mounted on the anodic side. The electrodes are in the form of fingered metal electrodes with the anodes of one bipolar unit interleaved between the cathodes of the next adjacent bipolar unit in the electrolyzer.

According to this invention, the anodes are removably mounted on the bipolar unit. This is accomplished by the use of an electrolyte resistant, acid resistant anode base member means having metal anodes mounted on and extending from one side of the base means, and an electroconductive, substantially hydrogen impermeable member bonded to the opposite side of the acid resistant anode base means. A threaded bolt is bonded to and extends from the hydrogen impermeable member through an aperture in the backplate to the cathodic surface of the backplate. The acid resistant anode base member is of larger diameter than the aperture in the backplate, whereby it may be held in compression against the backplate, providing an electrolyte tight seal between the backplate and the base member. Additionally, the hydrogen impermeable member and the threaded bolt provide electroconductivity from the cathodic surface of the backplate to the anode means.

DESCRIPTION OF THE INVENTION The invention may be understood by reference to the appended Figures. In the Figures:

FIG. 1 is a partially cut-away perspective view of a bipolar electrolyzer of one exemplification of this invention.

FIG. 2 is a cut-away side elevation of a bipolar electrolyzer of one exemplification of this invention.

' FIG. 3 is a partial cut-away plan view of a bipolar electrolyzer of one exemplification of this invention.

FIG. 4 is a partial cut-away view of a backplate of the bipolar electrolyzer of this invention taken along plane 4-4 of FIG. 3.

The bipolar electrolyzer l of this invention, useful for the production of alkali metal halate, contains a plurality of individual bipolar units 11 through 17 electrically and mechanically in series so that electrical current flows from an anode 41 attached to a first bipolar unit 17 of one cell 8 to a cathode 31 of that cell 8, attached to a second bipolar unit 16 of the cell 8. Electrical current passes from the cathode 31 through conducting means 45 of the bipolar unit 16 to an anode of the next adjacent cell 7 of the electrolyzer 1.

In the bipolar configuration shown in the Figures, the anodes 41 of a bipolar unit 17 are interleaved between the cathodes 31 of the next adjacent bipolar unit 16 and the cathodes 31 are interleaved between the anodes of the immediately preceding bipolar unit 17. The cathodes 31 of the one cell 9 and the anodes 41 of the next adjacent cell 8 constitute a common bipolar unit 17 with a backplate 20 therebetween. The current passes from the cathode 31 of the prior cell through the backplate 20 to the anode 41 of the next adjacent cell 8.

The backplate 20 has a cathodic surface 21 and an anodic surface 25 with electrolyte resistant means 27 on the anodic surface 25. The backplate 20 is fabricated of an electroconductive material with cathode means mounted on the cathode side 21 and anode means 31 mounted on the anodic side. The backplate 20 itself is an electrolyte resistant, electroconductive metal member having one surface 25 resistant to the anodic product and the opposite surface 21 resistant to the cathodic product. The backplate 20 may be fabricated of a material resistant to the cathodic product and to the electrolyte and having an anodic product, electrolyte resistant means 27 on the anodic side 25. Typical cathodic product resistant materials include cobalt, nickel, iron, steel or stainless steel. Most commonly, iron or steel will be used because of ready availability and lower costs.

The anodic product and electrolyte resistant means 27 on the opposite surface 25 of the backplate 20, may be a sheet or plate of an electrolyte resistant material mounted upon the cathode product resistant material backplate 25. For example, the surface of the backplate resistant to the anodic products and the electrolyte may be a valve metal sheet. The valve metals are those metals which form a corrosion resistant oxide upon exposure to either acidic media or to neutral media under anodic conditions. Such metals include titanium, zirconium, hafnium, vanadium, columbium, tantalum, and tungsten. Most commonly, when the electrolyte resistant anodic surface is provided by a valve metal, titanium will be utilized because of its low cost and ready availability relative to the other valve metals. However, it is to be understood that the other valve metals may be used in place thereof.

Alternatively, the anode product and electrolyte resistant means 27 may be provided by a rubber sheet 27 such as a natural rubber sheet, a low calcium ethylenepropylenediene rubber sheet, or a low calcium polystyrene sheet or a low calcium neoprene sheet or low calcium chloroprene sheet.

Cathode fingers 33 extend from the cathodic surface 21 of the backplate 20. The cathode fingers 33 are fabricated of a metal resistant to attack by the cathode products and the electrolyte. Typically, iron, cobalt, nickel, steel, or stainless steel may be used. Most commonly iron or steel is used.

The cathode fingers 33 may be metal sheets or plates. Alternatively the cathode fingers 33 may be perforate metal sheets or mesh.

The cathode fingers 33 may be welded, soldered, or otherwise permanently or semi-permanently joined to the cathodic surface 21 of the backplate 20 as shown in FIGS. 2, 3, and 4. Alternatively, the cathodes 33 may be mounted on a cathode base which is, in turn, bolted to the backplate 20. On the opposite side of the bipolar unit are anode fingers 43. In the bipolar electrolyzer of this invention, the anode fingers 43 are metal members having a suitable electroconductive surface thereon. The metal used in fabricating the anode fingers are the valve metals, i.e., those metals which form an oxide upon exposure to acidic or electrolytic media under anodic conditions. Such metals include titanium, zirconium, hafnium, vanadium, columbium, tantalum, and tungsten. Most commonly. titanium will be used for fabrication of the anodes of the electrolyzer of this invention because of the low cost and ready availability thereof.

The electroconductive surface on the anodes of this invention is a material characterized by a low chlorine overvoltage and a low oxygen overvoltage. Such materials include the platinum group metals such as ruthenium, rhodium, palladium, osmium, iridium, and platinum. Suitable electroconductive surfaces are also provided by the oxides of the platinum group metals such as ruthenium dioxide, rhodium trioxide, palladium dioxide, osmium dioxide, iridium trioxide, and platinum dioxide. Alternatively, the electroconductive surface on the anodes may be provided by an oxygencontaining compound of a platinum group metal such as an alkaline earth ruthenate, an alkaline earth ruthenite, an alkaline earth rhodate, an alkaline earth rhodite, a delafossite such as platinum cobalate, or palladium cobalate, or a pychloroe such as bismuth ruthenate or bismuth rhodate. Or, non-precious metal containing materials such as lead dioxide may be used to provide the anode surface.

The metal anodes 41 are in the form of metal fingers 43 extending outwardly from the backplate 20 toward the next adjacent bipolar unit in the electrolyzer 1. The individual anode fingers 43 may be solid plates or they may be perforate, foraminous, mesh or expanded mesh.

According to this invention, the anodes 41 are removably mounted on the electrolyte resistant backplate 20. This may be accomplished, according to this invention, by providing a backplate 20 with an aperture 29 therein suitable for carrying removable electroconductive anode support means 45.

The removable, electroconductive anode support means 45 includes an electrolyte resistant anode base member 47. The electrolyte resistant anode base mem ber 47 is larger than the aperture 29 in the backplate 20', that is, the electrolyte resistant anode base member 47, if circular, has a greater diameter than the aperture 29 if circular. Alternatively, if the aperture 29 or the electrolyte resistant anode base member 47 or both of them are non-circular in shape, than the smaller dimension perpendicular to the axis of the aperture, of the electrolyte resistant base member 47 is larger than the larger dimension of the aperture 20 perpendicular to the axis of the aperture, In this way an electrolyte tight seal is provided therebetween.

The metal anodes 43 are mounted on and extend away from one side of the electrolyte resistant anode base member 47. An electroconductive, substantially hydrogen impermeable member 49 is bonded to the opposite side of the electrolyte resistant anode base member 47 and corresponds in dimension to the aperture 29 in the backplate that is, the hydrogen impermeable member 49 fits within the aperture 29 in substantially concentric relationship therewith.

Threaded bolt means 51 extend from the hydrogen impermeable member 49 of the removable anode support means 45 through the aperture 29 in the backplate 20 to the cathodic surface 21 of the backplate 20. The threaded bolt means 51 is fabricated of an electroconductive, corrosion resistant, electrolyte resistantmaterial, so as to provide electrical conductivity between the backplate 20 and the anodes 41 while being substantially inert to attack by the electrolyte.

The acid resistant anode base member 47 is typically fabricated of a valve metal or film-forming metal as described hereinabove. The electroconductive, substantially hydrogen impermeable member 49 is fabricated of copper, lead, or aluminum. Copper is preferred. Copper is characterized by a low permeability to elemental hydrogen atoms and a high electroconductivity for the conduction of electrical current from the cathodes 31 and cathodic surface 21 of the backplate 20 to the electrolyte resistant base member 47.

The threaded bolt member 51, in the assembled bipolar unit includes nut means 53 for connecting the entire anode assembly, i.e., anode blades 43, electrolyte resistant anode base means 47, hydrogen impermeable electroconductive means 49, and threaded bolt means 51, to the bipolar unit. The threaded bolt means 51 extend from the hydrogen impermeable means 49 through the backplate to the cathodic surface 21. The threaded bolt means 49 are fabricated of material characterized by high shear strength, a high modulus of elasticity, and a high tensile strength so as to allow the nut means 53 to be applied thereto and to impose a high compressive force upon the electrolyte resistant surfaces 21 and 27 of the backplate 20.

In this way, electrical current can readily pass from the cathodic surface 21 of the bipolar unit through the anode support means 45 to the anode 41 with low electrical contact resistance voltage drop and low IR voltage drop. While the bolt means 51, the hydrogen impermeable electroconductive means 49, and the anode base means 47 may be joined together by any method known in the art such as threaded bolt means, welding, or soldering, they are preferably joined by friction welding whereby to provide a significantly reduced amount of contact resistance voltage drop within the anode support means 45.

The anode mounting means 45 including the electrolyte resistant anode base 47, the hydrogen impermeable electroconductive member 49, and the threaded means 51 are complimentary to and fit concentrically within the aperture 29 in the backplate 20.The anode base means 47 may be circular, or may be rectangular.

If rectangular, the individual anode blades 33 may bebonded to the sides thereof, for example by welding, soldering, or the like.

The anode base member 47 and the bolt means 51 impose a compressive force on the electrolyte resistant, acid resistant sheet 27 and the cathodic surface'21 of the backplate 20 thereby forming an electrolyte tight seal between the acid resistant base member 47 and the electrolyte resistant sheet 27 of the backplate 20. Typically, when the electrolyte resistant anode base 47 is titanium, the compressive force is on the order of 250 pounds per square inch, or higher, for example 300 or even.350 pounds per square inch. Inv this way, an electrolyte type seal, substantially immune to crevice corrosion, is obtained therebetween.

A gasket 61 may beinterposed between the electrolyte resistant sheet, 27 and the electrolyte resistant anode base member 47 so that compressive forces are imposed between the electrolyte resistant sheet 27 and the gasket 61 forming an electrolyte tight seal between the electrolyte resistant sheet 27 and the gasket 61. The compressive force is also imposed between the gasket 61 and the electrolyte resistant anode base member 47 forming a further electrolyte tight seal between the gasket 61 and the electrolyte resistant anode base member 47. In this way, the electroconductive, hydrogenimpermeable member 49 is substantially protected from contact with the electrolyte.

The gasket member 61 referred to hereinabove may be natural rubber, hard rubber, plastic, titanium, low calcium ethylene-propylene-diene rubber, low calcium polystyrene, low calcium neoprene, low calcium chloroprene, or the like.

The bipolar units 11 through 17 are electrically in series with the anodic side 25 of one bipolar unit 17 and the cathodic side 21 of the next adjacent bipolar unit 16 forming an individual electrolytic cell 8 therebetween. The anodes 41 of one bipolar unit 17 are interleaved between the cathodes 31 of the next adjacent bipolar unit 16 and are substantially parallel to each other.

The anodes 41 and the cathodes 31 may both be perpendicular to the bipolar units. Alternatively, they may form an angle therewith and a complimentary angle with the facing bipolar unit so as to provide parallel electrodes. The facing bipolar units in a single individual cell are in' a'single electrolyte chamber so as to, provide for the formation of the alkali metal halate.

The electrolyzer contains a number of individual bipolar units, e.g., three or five or more, for example, as many as or or even or more bipolar units forming bipolar cells. The individual bipolar cells have an electrolyte volume suffieient to provide a retention time of from about 40 to about 250 milliliters per Am: pere and preferably from about 65 to about 200 milliliters per Ampere, whereby to chemically form the alkali metal halate within the cell.

Typically, in the electrolytic cell of this invention, the inter electrode gap between the anodes of one bipolar unit in the cathodes of the next adjacent bipolar unit within a single bipolar cell will be about one-eighth to about one-fourth of an inch with the anodes and cathodes of the individual cell being separated from each other by ceramic or plastic rivets 71 press fitted into the cathode fingers. In this way, a compact volume is provided for actual electrolysis. Moreover, a large cell body may be used, thereby providing a large volume'for halate-forming reactions. In this way, a higher concentration of alkali metal halate may be formed within the electrolyte, in which case a lower cooling requirement is imposed upon the cell and higher cell efficiency is obtained. Additionally, a brine feed may be used rather than a solid salt feed.

The electrolytic cell of this invention may be used for the electrolysis of alkali metal halides to yield alkali metal halides. Typically, sodium chloride may be electrolyzed to yield sodium chlorate, sodium bromide may be electrolyzed to yield sodium bromate, potassium chloride may be electrolyzedto yield potassium chlorate, and potassium bromide may be electrolyzed to yield potassium bromate.

In the operation of this cell, a saturated brine feed, for example, a feed of 300 to 325 grams per liter of sodium chloride may be fed to the electrolyzer 1. The brine feed may either be parallel, i.e., individual brine feed to each individual electrolytic cell in a cell series, or the brine feed may be in series, i.e., at one point in the cell with cell liquor removal at a distant point in the cell from the brine feed. Series feed is preferred, as the feed to thefirst cell is low in hypochlorite ion concentration, thereby providing a high degree of chemical formation of chlorate ion and a high current efficiency. An electromotive force is imposed across the bipolar electrolyzer, thereby causing electrical current to flow through the bipolar electrolyzer as described above. Electrolysis may then be conducted at a current density of above 200 Amperes per square foot, for example, as high as 400 or 600 Amperes per square foot or even higher. With a cell retention time from about 40 to about 250 milliliters per Ampere and preferably about 65 to about 200 milliliters per Ampere, a cell liquor is obtained having a pH of from about 5.6 to about 6.8 and preferably from about 6.0 to about 6.7. The cell liquor temperature within the cell is from about 50C to about 100C, generally in excess of about 80C and frequently as high as 95C, or 98C, or even 100C. A cell liquor is obtained containing from about 650 to about 750 grams per liter of sodium chlorate, about 60 to about 75 grams per liter of sodium chloride, from about 1 to about 4 grams per liter of sodium dichromate and from about 1 to about 3 grams per liter of sodium hypochlorite.

Although the present invention has been described with reference to specific details of particular embodiments thereof, it is not intended thereby to limit the scope of the invention, except insofar as specific details comprises:

an acid resistant anode base member larger than said aperture; finger-like metal anodes mounted on and extending from one side of said acid resistant anode base member; an electroconductive, substantially hydrogen impermeable copper member friction welded to the opposite side of said acid resistant anode base and corresponding to the aperture in the backplate; and threaded bolt means friction Welded to and extending from the hydrogen impermeable copper member through said aperture to the cathodic surface of the backplate and means for securing said anode means and said backplate in electrolyte impermeable, electroconductive contact. 2. The bipolar electrolyzer of claim 1 wherein said backplate comprises an alkali resistant structural memv .ber and an acid resistant sheet on the anodic side of said structural member, and wherein said anode base member applies a compressive force on said acid resistant sheet thereby forming an electrolyte tight seal between said acid resistant anode base member and said acid resistant sheet.

3. The bipolar electrolyzer of claim 2 wherein a gasket is interposed between said acid resistant sheet and said acid resistant anode base member, and wherein compressive forces are imposed between said gasket and said acid resistant anode base member forming an electrolyte tight seal therebetween.

4. The bipolar electrolyzer of claim 1 wherein the anode means of one bipolar unit and the cathode means of the next adjacent bipolar unit are in the same electrolyte compartment.

5. In a bipolar electrolyzer having a plurality of individual bipolar units in series, each of said individual bipolar units including a backplate having an aperture extending therethrough, a steel cathodic surface, cathode means mounted on and extending from said cathodic surface, a titanium anodic surface, and anode means extending from said anodic surface, whereby the anode means of one bipolar unit and the cathode means of the next adjacent bipolar unit are in the same electrolyte compartment, the improvement wherein said anode means is removable independently of said cathode means and comprises:

a titanium anode base member larger than said aperture; finger-like metal anodes mounted on and extending from one side of said titanium anode base member; an electroconductive, substantially hydrogen impermeable copper member friction welded to the opposite .side of said acid resistant anode base and corresponding to the aperture in the backplate; and threaded bolt means friction welded to and extending fromthe hydrogen impermeable copper member through said aperture to the cathodic surface of the backplate, whereby said anode base member applies a compressive force on the titanium anodic surface of said backplate thereby forming an electrolyte tight seal between said titanium anode base member and said backplate. 6. A bipolar electrolyzer having a plurality of individual bipolar units in series, each of said individual bipolar units including a backplate having a cathodic surface and an anodic surface and being provided with a countersunk aperture extending through said backplate between said surfaces,

at least one cathode member secured to said backplate and extending laterally from the cathode surface thereof,

an electroconductive, substantially hydrogen impermeable copper member disposed within said aperture in contact with the countersunk surface thereof,

an acid resistant anode base member having opposing surfaces overlying and extending beyond the edge of said aperture, said anode base member being secured on one surface to said copper memher, 7

a plurality of anode members secured to said anode base member and extending laterally from the surface, of said anode base member opposing the surface of said base member to which the copper member is secured,

force thereon and on said copper member to clamp said copper member and anode base member to said backplate whereby to seal the aperture therein against the flow of liquids and gases therethrough. 

1. In a bipolar electrolyzer having a plurality of individual bipolar units in series, each of said individual bipolar units including a backplate having an aperture extending therethrough, a cathodic surface, cathode means mounted on and extending from said cathodic surface, an anolyte resistant surface, and anode means extending from said anolyte resistant surface, the improvement wherein said anode means is detachably supported independently of said cathode means and comprises: an acid resistant anode base member larger than said aperture; finger-like metal anodes mounted on and extending from one side of said acid resistant anode base member; an electroconductive, substantially hydrogen impermeable copper member friction welded to the opposite side of said acid resistant anode base and corresponding to the aperture in the backplate; and threaded bolt means friction welded to and extending from the hydrogen impermeable copper member through said aperture to the cathodic surface of the backplate and means for securing said anode means and said backplate in electrolyte impermeable, electroconductive contact.
 2. The bipolar electrolyzer of claim 1 wherein said backplate comprises an alkali resistant structural member and an acid resistant sheet on the anodic side of said structural member, and wherein said anode base member applies a compressive force on said acid resistant sheet thereby forming an electrolyte tight seal between said acid resistant anode base member and said acid resistant sheet.
 3. The bipolar electrolyzer of claim 2 wherein a gasket is interposed between said acid resistant sheet and said acid resistant anode base member, and wherein compressive forces are imposed between said gasket and said acid resistant anode base member forming an electrolyte tight seal therebetween.
 4. The bipolar electrolyzer of claim 1 wherein the anode means of one bipolar unit and the cathode means of the next adjacent bipolar unit are in the same electrolyte compartment.
 5. IN A BIPOLAR ELECTROLYZER HAVING A PLURALITY OF INDIVIDUAL BIPOLAR UNITS IN SERIES, EACH OF SAID INDIVIDUAL BIPOLAR UNITS INCLUDING A BACKPLATE HAVING AN APERTURE EXTENDING THERETHROUGH, A STEEL CATHOFIC SURFACE, CATHODE MEANS MOUNTED ON AND EXTENDING FROM SAID CATHODIC SURFACE, A TITANIUM ANODIC SURFACE, AND ANODE MEANS EXTENDING FROM SAID ANODIC SURFACE, WHEREBY THE ANODE MEANS OF ONE BIPOLAR UNIT AND THE CATHODE MEANS OF THE NEXT ADJACENT BIPOLAR UNIT ARE IN THE SAME ELECTROLYTE COMPARTMENT, THE IMPROVEMENT WHEREIN SAID ANODE MEANS IS REMOVABLE INDEPENDENTLY OF SAID CATHODE MEANS AND COMPRISES: A TITANIUM ANODE BASE MEMBER LARGER THAN SAID APERTURE, FINGER-LIKE METAL ANODES MOUNTED ON AND EXTENDING FROM ONE SIDE OF SAID TITANIUM ANODE BASE MEMBER, AN ELECTROCONDUCTIVE, SUBSTANTIALLY HYDROGEN IMPERMEABLE COPPER MEMBER FRICTION WELDED TO THE OPPOSITE SIDE OF SAID ACID RESISTANT ANODE BASE AND CORRESPONDING TO THE APERTURE IN THE BACKPLATE, AND THREADED BOLT MEANS FRICTION WELDED TO AND EXTENDING FROM THE HYDROGEN IMPERMEABLE COPPER MEMBER THROUGH SAID APERTURE TO THE CATHODIC SURFACE OF THE BACKPLATE, WHEREBY SAID ANODE BASE MEMBER APPLIES A COMPRESSIVE FORCE ON THE TITANIUM ANODIC SURFACE OF SAID BACKPLATE THEREBY FORMING AN ELECTROLYTE TIGHT SEAL BETWEEN SAID TITANIUM ANODE BASE MEMBER AND SAID BACKPLATE.
 6. A bipolar electrolyzer having a plurality of individual bipolar units in series, each of said individual bipolar units including a backplate having a cathodic surface and an anodic surface and being provided with a countersunk aperture extending through said backplate between said surfaces, at least one cathode member secured to said backplate and extending laterally from the cathode surface thereof, an electroconductive, substantially hydrogen impermeable copper member disposed within said aperture in contact with the countersunk surface thereof, an acid resistant anode base member having opposing surfaces overlying and extending beyond the edge of said aperture, said anode base member being secured on one surface to said copper member, a plurality of anode members secured to said anode base member and extending laterally from the surface, of said anode base member opposing the surface of said base member to which the copper member is secured, a rod-like member secured to the surface of said copper base member adjacent said backplate, said rod-like member being adapted to extend through said aperture toward the cathode surface of the backplate; and means engaging said rod-like member for exerting a force thereon and on said copper member to clamp said copper member and anode base member to said backplate whereby to seal the aperture therein against the flow of liquids and gases therethrough. 